The present invention relates to a rotary electric machine and a method for mounting a coil on a core for a rotary electric machine.
A typical rotary electric machine such as a motor and a generator is formed by disposing a coil onto a core that is used for a rotary electric machine, in which a stator (or a rotor) is formed of laminated steel sheets. For example, when a stator core is used, teeth are formed in the inner circumferential surface (or outer circumferential surface) of the stator core and a stator is formed by inserting a coil in slots formed between the teeth. The coil is formed from a conductive wire insulated with a coating. Conventionally, wires having a circular cross-section have been used. However, wires having a flat cross-section such as oval or rectangular have come into use as described in Japanese Laid-Open Patent Publication No. 10-66314 to improve the output characteristics of the rotary electric machine by increasing the density (lamination factor) of the coil in each slot. In this case, the number of coil side wires inserted in each slot may be increased in order to optimize the operating condition of the rotary electric machine.
Japanese Laid-Open Patent Publication No. 10-66314 discloses coil pieces formed before being mounted onto the stator. Each coil piece is formed by winding wire having rectangular cross section, such that coil sides, each of which is a section inserted in a slot opening, and coil ends, each of which is not inserted in the slot, are arranged to appear alternatively as the wire is wound in a spiral form. The coil is mounted on the stator core by inserting the coil side wires into the corresponding slot through an open end of the slot. Each coil piece is formed into a shape in which adjacent coil side wires (and adjacent coil end wires) abut each other on the narrower sides of the rectangular cross section of the wire and the wider sides of the wire side faces together form a substantially planar surface.
According to the method for mounting a coil described in Japanese Laid-Open Patent Publication No. 10-66314, the coil pieces connected by the connecting wire are formed in advance with a twisted portion. One coil side of each of two coil pieces are then inserted into one slot successively such that two coil pieces are disposed next to each other in the circumferential direction of the stator core. That is, the coil side wires of each coil piece inserted in the slot overlap along the radial direction of the stator core in the slot. Therefore, the coil side wires of the second coil piece are laminated consecutively onto the coil side wires of the first coil piece in the radial direction of the stator core.
The above described coil can permit the coil side wires to be inserted in the slots without being hindered, even if the open end of each slot is somewhat narrowed by a projection extending toward the circumferential direction of the stator from the distal end of each tooth as described in Japanese Laid-Open Patent Publication No. 2003-204647.
However, when the coil pieces of the Japanese Laid-Open Patent Publication No. 10-66314 are used in some slots where the open end of each slot is narrowed, the coil side wires of the coil piece that has earlier been inserted in the slot might block the opening of the slot from inside depending on the position and shape of the openings. This might obstruct insertion of the subsequent coil pieces into the slot. Therefore, according to the method for mounting a coil described in Japanese Laid-Open Patent Publication No. 10-66314, the number of coils that are inserted in each slot cannot be increased in some positions where the opening of each slot is narrow. If so, as the lamination factor of the coils in each slot cannot be improved, the output characteristics of the rotary electric machine cannot be improved as desired.
Japanese Laid-Open Patent Publication No. 2003-204647 discloses a number of U-shaped coil pieces, each coil piece being inserted in the slot from the axial direction of the stator core such that both leg portions of each coil piece (coil sides) are laminated in the radial direction of the stator core while sandwiching one of the teeth from both sides. In this manner, the coil pieces are temporarily mounted in the slots. Subsequently, the distal ends of the leg portions (coil ends) of the coil pieces that project axially outward from the slots are connected by TIG welding or the like such that the laminated coil pieces are connected in a spiral form. As a result, a coil is formed.
According to the method for mounting the coil described in Japanese Laid-Open Patent Publication No. 2003-204647, various types of U-shaped coil pieces with various sizes are prepared. Leg portions (coil sides) of the coil pieces are successively inserted in a single slot such that the leg portions are sequentially laminated in the circumferential direction of the stator core.
The method for mounting the coil described in Japanese Laid-Open Patent Publication No. 2003-204647 reduces the risk that the legs (coil sides) of the previously mounted coil pieces will obstruct other coil pieces that are subsequently mounted (inserted). However, the method requires a complicated operation for connecting the distal ends of the legs of the coil pieces through welding or the like after temporarily mounting the coil pieces to the slots. This reduces production efficiency.